<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>一起来看流星雨</title>
<script>
var context;
var arr = new Array();
var starCount = 800;
var rains = new Array();
var rainCount =20;
//初始化画布及context
function init(){
//获取canvas
var stars = document.getElementById("stars");
windowWidth = window.innerWidth; //当前的窗口的高度
stars.width=windowWidth;
stars.height=window.innerHeight;
//获取context
context = stars.getContext("2d");
}
//创建一个星星对象
var Star = function (){
this.x = windowWidth * Math.random();//横坐标
this.y = 5000 * Math.random();//纵坐标
this.text=".";//文本
this.color = "white";//颜色
//产生随机颜色
this.getColor=function(){
var _r = Math.random();
if(_r<0.5){
this.color = "#333";
}else{
this.color = "white";
}
}
//初始化
this.init=function(){
this.getColor();
}
//绘制
this.draw=function(){
context.fillStyle=this.color;
context.fillText(this.text,this.x,this.y);
}
}
//画月亮
function drawMoon(){
var moon = new Image();
moon.src = "./images/moon.jpg"
context.drawImage(moon,-5,-10);
}
//页面加载的时候
window.onload = function() {
init();
//画星星
for (var i=0;i<starCount;i++) {
var star = new Star();
star.init();
star.draw();
arr.push(star);
}
//画流星
for (var i=0;i<rainCount;i++) {
var rain = new MeteorRain();
rain.init();
rain.draw();
rains.push(rain);
}
drawMoon();//绘制月亮
playStars();//绘制闪动的星星
playRains();//绘制流星

}
//星星闪起来
function playStars(){
for (var n = 0; n < starCount; n++){ 
arr[n].getColor(); 
arr[n].draw(); 
} 

setTimeout("playStars()",100);
}

/*流星雨开始*/
var MeteorRain = function(){
this.x = -1;
this.y = -1;
this.length = -1;//长度
this.angle = 30; //倾斜角度
this.width = -1;//宽度
this.height = -1;//高度
this.speed = 1;//速度
this.offset_x = -1;//横轴移动偏移量
this.offset_y = -1;//纵轴移动偏移量
this.alpha = 1; //透明度
this.color1 = "";//流星的色彩
this.color2 = ""; //流星的色彩
/****************初始化函数********************/
this.init = function () //初始化
{
this.getPos();
this.alpha = 1;//透明度
this.getRandomColor();
//最小长度，最大长度
var x = Math.random() * 80 + 150;
this.length = Math.ceil(x);
// x = Math.random()*10+30;
this.angle = 30; //流星倾斜角
x = Math.random()+0.5;
this.speed = Math.ceil(x); //流星的速度
var cos = Math.cos(this.angle*3.14/180);
var sin = Math.sin(this.angle*3.14/180) ;
this.width = this.length*cos ; //流星所占宽度
this.height = this.length*sin ;//流星所占高度
this.offset_x = this.speed*cos ;
this.offset_y = this.speed*sin;
}
/**************获取随机颜色函数*****************/
this.getRandomColor = function (){
var a = Math.ceil(255-240* Math.random()); 
//中段颜色
this.color1 = "rgba("+a+","+a+","+a+",1)";
//结束颜色
this.color2 = "black";
}
/***************重新计算流星坐标的函数******************/
this.countPos = function ()//
{
//往左下移动,x减少，y增加
this.x = this.x - this.offset_x;
this.y = this.y + this.offset_y;
}
/*****************获取随机坐标的函数*****************/
this.getPos = function () //
{
//横坐标200--1200
this.x = Math.random() * window.innerWidth; //窗口高度
//纵坐标小于600
this.y = Math.random() * window.innerHeight; //窗口宽度
}
/****绘制流星***************************/
this.draw = function () //绘制一个流星的函数
{
context.save();
context.beginPath();
context.lineWidth = 1; //宽度
context.globalAlpha = this.alpha; //设置透明度
//创建横向渐变颜色,起点坐标至终点坐标
var line = context.createLinearGradient(this.x, this.y, 
this.x + this.width, 
this.y - this.height);
//分段设置颜色
line.addColorStop(0, "white");
line.addColorStop(0.3, this.color1);
line.addColorStop(0.6, this.color2);
context.strokeStyle = line;
//起点
context.moveTo(this.x, this.y);
//终点
context.lineTo(this.x + this.width, this.y - this.height);
context.closePath();
context.stroke();
context.restore();
}
this.move = function(){
//清空流星像素
var x = this.x+this.width-this.offset_x;
var y = this.y-this.height;
context.clearRect(x-3,y-3,this.offset_x+5,this.offset_y+5); 
// context.strokeStyle="red";
// context.strokeRect(x,y-1,this.offset_x+1,this.offset_y+1);
//重新计算位置，往左下移动
this.countPos();
//透明度增加
this.alpha -= 0.002;
//重绘
this.draw(); 
}
}
//绘制流星
function playRains(){

for (var n = 0; n < rainCount; n++){ 
var rain = rains[n];
rain.move();//移动
if(rain.y>window.innerHeight){//超出界限后重来
context.clearRect(rain.x,rain.y-rain.height,rain.width,rain.height);
rains[n] = new MeteorRain();
rains[n].init();
}
} 
setTimeout("playRains()",2);
}
/*流星雨结束*/
</script>
<style type="text/css">
body{
background-color: black;
}
body,html{width:100%;height:100%;overflow:hidden;}
</style>
</head>
<body>
<canvas id="stars"></canvas>
</body>
</html>